Bass ports, a good thing or a bad thing?

[Bill@WelcomeHome]

speaker cabinet design is a combination of compromises balancing price point and performance and size. Anyone who tries to generally proclaim that if a cabinet has a port or not is the determining factor as to how good or bad the cabinet sounds is an idiot showing how little he knows about the subject. You can make some general assumptions based on -any- part of a cabinet design which, without taking the entire design and final sound in to account, is meaningless blather.

[Chrisc_o]

Exactly. The port is part of a carefully calculated system. You can't objectively judge how the whole system works by looking only at a single element.

[joelpatterson]

Far be it from me to second guess the design genius of design geniuses... but it seems like about half the time, I plug up the ports and the speakers sound better.

As in "better"-- more focused, less diffuse, more solid and more energetic and crisper.

[piper]

Here's what a port does: It makes the box resonate at a lower frequency.

Depending on the exact design, the port could make the box have a sharp hump at a particular frequency, or it could be a gentle, smooth extension.

In order to sound good, the resonances of the speaker and the box need to suit each other.

[bruvvamoff]

OK I'll elaborate. If you took a monitor that had a bass port, and plugged it up, what would the difference be in the frequency response?

[Bill@WelcomeHome]

Originally Posted by bruvvamoff

OK I'll elaborate. If you took a monitor that had a bass port, and plugged it up, what would the difference be in the frequency response?

Once again, you cannot generalize. Without knowing exact details, you are just guessing. (And the results would probably vary over SPLs... don't forget, the room is going to play a part in what you hear and changing the SPLs will excite the room differently.) The poster who liked the results of plugging them up... how scientific is the result? And are we talking about in a specific room?

Meanwhile, the ATC SCM-25A comes with plugs for the ports and they tell you the effect, so that you know what will happen. I don't think I've ever seen that before.

[Silent Sound]

Ports do some interesting things. They can extend the bass response of the monitors, but to do so, they'll usually have to make some compromises. Because the sound from the port is coming out of the back of the speaker, the sound out of the port could be 180º out of phase of the sound coming out the front. However, by "tuning" the cabinet, the designer can take this into consideration and use it to their advantage. In doing so, they have to make some compromises, especially in the crossover frequencies and things like time domain. But to say that makes ports a bad idea would be like saying using two way speaker with a separate tweeter and woofer is a bad idea. There's a lot more going into this than I care to explain or even fully understand, but suffice it to say that ports can be a good thing or a bad thing depending on how they are implemented. So just use your ears and get a set of monitors that sound good. Whether they are ported design or have an infinite baffle doesn't really matter compared to how they sound.

My experience? I have a set of Tannoy Reveals. In two houses I lived in, I plugged up the port holes and used a sub. Why? Because it produced a more accurate sound in my listening position (tested using a frequency sweep generator). Recently, I moved into a new house and when I set up my monitors in my new room, I discovered they sounded more accurate throughout the lower frequencies with the port holes open. I still use the subwoofer, but for whatever reason, it works better in this room with this setup.

[Phosphate]

Originally Posted by Bill@WelcomeHome

The poster who liked the results of plugging them up... how scientific is the result? And are we talking about in a specific room?

His results were not scientific, but were likely based on how well the mix translated after blocking the ports. I'm sure it's very room specific, walls can reflect the bass very nasty. One example is my current setup, where my HS80M's get a little bit too much boom and rattling frequencies from the loose 70's wood paneling that lies right behind the bass ports. I ought to get something for behind my monitors, if anyone has any ideas please give 'em to me!

[piper]

Originally Posted by bruvvamoff

OK I'll elaborate. If you took a monitor that had a bass port, and plugged it up, what would the difference be in the frequency response?

In most cases there will be less bass.

How much and where depends on the design.

I remember a nifty design with two exterior ports and an interior port. The box was therefore tuned to three different frequencies at once.

[tINY]

I guess I'm an idiot...

For studio monitors and home listening, I do not like ports. I tollerate them on main monitors when there is a good (sealed box) sub.

Ports are interesing things... They can extend the flat response of unequalized woofers by adding a resonator. This helps if you are limited on amplifier power, or you have inexpensive drivers that won't take a lot of power.

What price do you pay? Transient response is degraded - remember that the port is 90deg out of phase with the driver at it's resonance frequency. Also, deep bass is sacrificed - below the port frequency, the response rolls off at 24dB/octave instead of 12dB/octave.

Generally, I like the more accurate transients with better deep bass that you get from sealed woofers. And, since powerful amps and decent equalizers are pretty cheap these days, I don't see the need for ports when cabinets size isn't an issue.

Displacement limitations are another issue, but I'd rather add more woofers than deal with the ports on playback systems.




-tINY

[joelpatterson]

Originally Posted by Bill@WelcomeHome

... who liked the results of plugging them up... how scientific is the result? ....

Ridiculously scientific! I heard it with my own ears!

On the other hand, I made a set of speakers with my son from a detailed design on... hmmm, it was some website... and the precisely calibrated ports they called for, countersinking the edges of the PVC pipe and everything, worked a particular kind of eerie magic all their own... no matter where you were in the room, and no matter which way the speakers were facing, the sound was awesomely articulately clear. It was sort of stunning.

Whereas... I dunno, something about lots of these ported speakers seem gimmicky, like "we can prove the bass response is enhanced!" but it's a false, deceptive effect, a phony trick...

[bruvvamoff]

Ports are interesing things... They can extend the flat response of unequalized woofers by adding a resonator. This helps if you are limited on amplifier power, or you have inexpensive drivers that won't take a lot of power.

What price do you pay? Transient response is degraded - remember that the port is 90deg out of phase with the driver at it's resonance frequency. Also, deep bass is sacrificed - below the port frequency, the response rolls off at 24dB/octave instead of 12dB/octave.

This response, helpful and interesting.

speaker cabinet design is a combination of compromises balancing price point and performance and size. Anyone who tries to generally proclaim that if a cabinet has a port or not is the determining factor as to how good or bad the cabinet sounds is an idiot showing how little he knows about the subject. You can make some general assumptions based on -any- part of a cabinet design which, without taking the entire design and final sound in to account, is meaningless blather.

This one, unhelpful and dull.

Thanks all.

[Nick Hamilton]

Another thing about ported designs is it allows the speaker to push more air out of the box, sealed or non-ported designs need more amplifier power to achieve the same SPL levels.

I have also plugged the holes in some monitors and found that the transient response got better as mentioned above.

[IdiotManchild]

It's not necessarily good or bad to have ports or not.

A well designed loudspeaker with a ported cabinet will sound better than a poorly thought out sealed cabinet design.

[PhilDW]

Get hold of a waterfall graph for the monitor. You don't want the bass port to cause bass frequencies to resonate on longer than they should. NS10s are good in this regard (they don't resonate), so are Auratones, that should say something about why these have been popular choices. That's not about a consensus of what people think, that's a measurable effect, so ignore consensus and find a waterfall for the monitor you want.

I see many people asking about extra bass extension in their monitors, so I suspect the manufacturers may be catering to this, but bass accuracy is difficult enough as it is without monitors exaggerating bass, ported or not.

[chescat]

I just added bass ports to my vintage electrostats using utility tape rolls and utility tape & I LOOOVVVEEE the results..!!! From VERY GOOD speakers to TO DIE FOR..!!!!

[Bill@WelcomeHome]

It's funny... the four most written and talked about monitors for under $10,000 each uses a different design. The ATC uses a port. The Focal SM9 uses a passive radiator. The Barefoot MM27 uses a unique dual sub sealed cabinet design. The Trident HG-3 uses two boxes, one a rotating pod. These are considered to be the best sounding in the price range. The ATCs are roundly touted for the accuracy of the mids, yet another poster who has not heard them says that the design of the mids and tweeters has to cause distortion. My own and my friends listening hears no obvious problem with the ported low end, yet we declare here that ports must be universally bad. Passive radiators always get a bad rap, yet reviewers are raving about the low end of the Focal SM9s. Users have left the MM27s for the ATCs, the ATCs for the MM27s, listeners claim the HG-3s sound best, but the SM9s are the newest buzz.

which is why I said originally, we cannot take a single aspect of cabinet design and condemn all products attempting to use that aspect. Speaker cabinet design is a balance of compromises and decisions. Done well is done well.

[tINY]

Remember, too, that most small and home studios generally don't have low-frequency room response well controlled. Add in the fact that our brains fairly quickly adapt to non-flat response (ie, filter out the room curve in our heads) and all you are left with is how that particular model interacts with that room.

If there are no major ringings or gross deficiencies (like a big wide null at the listening position), then people think it sounds good.

Far and away, the distortions of the mid and upper frequencies are what make the difference between mediocre and good monitors.




-tINY

[basmartin]

Originally Posted by joelpatterson

Far be it from me to second guess the design genius of design geniuses... but it seems like about half the time, I plug up the ports and the speakers sound better.

As in "better"-- more focused, less diffuse, more solid and more energetic and crisper.

I agree 100%.

[joelpatterson]

Then we have 200% agreement. I think that settles it.

[bruvvamoff]

So, should the acoustic treatment of a small room be given a different approach when the monitors have bass ports.
For instance, my HS80's have ports at the back.
Does that mean I should put bass traps behind the monitors, or catch the soundwaves on the rebound at the back of the room behind me?

[tINY]

Won't matter, really. Position of the speakers is more important in small rooms.

Position of bass traps in a small room: Anywhere you can cram one, put one, then put a couple more in any remaining corner.




-tINY

[piper]

Originally Posted by bruvvamoff

Ports are interesing things... They can extend the flat response of unequalized woofers by adding a resonator.

To clarify, the port changes the resonance frequency of the box, and the Q.

[barefoot]

Here’s something I posted a while ago in another thread.

Originally Posted by barefoot

Every speaker in a box is essentially a high pass filter. And such filters naturally impart group delay (phase distortion) in the neighborhood of their low frequency cutoff. Higher group delay means worse transient response, time smearing, muddiness or whatever you like to call it. Sharper filters have higher group delay. So here’s the breakdown of cabinet types:

Sealed cabinet: 2nd order high-pass, 12 dB/octave roll off.
Ported: 4th order high-pass, 24 dB/octave roll off.
Passive Radiator: 6th order high-pass, 36 dB/octave roll off.

So for a given -3dB cutoff frequency a sealed cabinet will have the lowest group delay and the most low frequency extension. A passive radiator will have the highest group delay and the least low frequency extension.

The reason this is the case is because ports and passive radiators are acoustic resonators. Resonators store and releases energy over time, hence the delay. These types of speakers lower the driver’s cutoff frequency by coupling it to a low frequency resonator. The resonator has a bell shaped resonant peak which tails off at higher and lower frequencies. So you tune the resonator below the natural cutoff of the driver in such a way that the driver begins to excite the upper tail of the resonant curve just as its own output begins to drop. This boosts the overall output and extends the low frequency. As frequency decreases more the driver output drops more. But now it's closer to the resonant peak of the port/PR. So the overall output stays flat because the port/PR is more excited. Below the resonant peak the system output drops precipitously. The driver also has very little acoustic loading from the cabinet (springiness) below the port resonance frequency and tends to be poorly controlled.

Of course, there are gray areas in all of these approaches. A passive sealed speaker in a very small box can have a high Q and exhibit relatively poor transient response. A ported speaker with a very large cabinet can have transient response closer to that of a sealed design. Conversely, a ported speaker with a small cabinet and low tuning frequency will behave more like a passive radiator. And a passive radiator design with a large cabinet and a light dummy cone will behave more like a ported speaker. So, there are many ways to skin the cat.

I would guess that a significant percentage of speakers out there lean towards the third scenario I mentioned above. They use rather small cabinets tuned to optimistically low frequencies - probably for the sake of getting those bass cutoff specs as low as possible. This typically results in poor transient behavior and copious amounts of distortion at relatively low volume levels. The sonic merits of such designs are for you to judge.

Cheers!
Thomas

[tINY]

Good summary, Barefoot.



-tINY

[bruvvamoff]

Originally Posted by barefoot

Here’s something I posted a while ago in another thread.


Of course, there are gray areas in all of these approaches. A passive sealed speaker in a very small box can have a high Q and exhibit relatively poor transient response. A ported speaker with a very large cabinet can have transient response closer to that of a sealed design. Conversely, a ported speaker with a small cabinet and low tuning frequency will behave more like a passive radiator. And a passive radiator design with a large cabinet and a light dummy cone will behave more like a ported speaker. So, there are many ways to skin the cat.

I would guess that a significant percentage of speakers out there lean towards the third scenario I mentioned above. They use rather small cabinets tuned to optimistically low frequencies - probably for the sake of getting those bass cutoff specs as low as possible. This typically results in poor transient behavior and copious amounts of distortion at relatively low volume levels. The sonic merits of such designs are for you to judge.

Cheers!
Thomas

Every now and then I read a post that makes everything so clear in an interesting way that I actually smile.
This is one such post.

[Fleaman]

Yes, excellent post by Thomas.

I always cringe at all the 'sealed' is always better posts, etc., etc. ---it's a way oversimplified comment.

Monitor design is about trade-offs, and monitor designers like Harvey and Thomas confirm that over and over here on GS....

[Omega Arts]

I got here from another post I made and this helps me some. My Genelec 1031a of course are ported. I was setting at the desk mixing and thinking the bass has never been to my liking on these monitors. I also have NS 10's and Auroatones and a sub. I rarely use the sub.
SOO I got up and taped up the ports and immediately I could hear the bass correctly.
I'm thinking could this be right. I could hear everything better.

I'm still adjusting the acoustics in this control room and would think just a bad response in the room( probably true) EXCEPT I've used these Genny's in three different rooms and had the same opinion.

I'm going to do a quick mix of something with the ports covered and see how it translates and I'll give an opinion later.

I have a set of KRK Rokit 8's I use on my little writing set up at home and brought them to the studio and these things are all over the place.
No go for me.

[bruvvamoff]

Originally Posted by Omega Arts

I got here from another post I made and this helps me some. My Genelec 1031a of course are ported. I was setting at the desk mixing and thinking the bass has never been to my liking on these monitors. I also have NS 10's and Auroatones and a sub. I rarely use the sub.
SOO I got up and taped up the ports and immediately I could hear the bass correctly.
I'm thinking could this be right. I could hear everything better.

I'm still adjusting the acoustics in this control room and would think just a bad response in the room( probably true) EXCEPT I've used these Genny's in three different rooms and had the same opinion.

I'm going to do a quick mix of something with the ports covered and see how it translates and I'll give an opinion later.

I have a set of KRK Rokit 8's I use on my little writing set up at home and brought them to the studio and these things are all over the place.
No go for me.

Rokits have a terrible rep.
I've never tested them so I can't comment.
I'm going to get used to these Yams with the bass port left alone.
If my mixes are persistently strange in the low frequencies then I'll try covering them.